Added research doc for named types

doc/research/named_field_types.md

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+# Named query field types
+
+A higher level version of the query field type. Through configuration, queries are associated to a name. Those are added added to the list of available field types. When added, they query type isn't show, and the parameters are immediately displayed for editing. It saves time when modelling the content by allowing to reuse the same type for a similar concept.
+
+## Examples
+
+```
+ezplatform:
+  named_query_types:
+    children:
+      query_type: eZ:Children
+      default_parameters:
+        location: '@=location'
+        type: '@=returnedType'
+    relating_content:
+      query_type: eZ:ContentRelatedTo
+      default_parameters:
+        to_content: '@=content'
+        type: '@=returnedType'
+```
+
+## Extra features
+
+### Default query type parameters
+
+Content and location level (not field) based parameters can get a default value: the current content, its section, the returned type...
+
+### Translation
+
+That extra layer is a good place for translating parameters.
+
+### Customization
+
+Custom templates could be associated to named query field types, giving extra flexibility.
+
+### Extensibiliy
+
+Named queries make it easy for 3rd parties to add their own field types without developing any:
+
+- define new query types, with custom criteria if needed
+- define named queries
+